1. Field of the Invention
This invention relates to methods of consolidating solids in the vicinity of a wellbore and more particularly relates to the consolidation of incompetent formations utilizing resinous compositions and a rapid acting catalyst.
2. Description of the Prior Art
Sand consolidation is a near wellbore treatment of a well to be tested or placed in production. Surrounding a wellbore in many instances are incompetent highly porous and fragmentable sand or particulate formations. Under production conditions, the particulate is often displaced from its aggregated structure and carried along by a fluid flowing to a producing well. If the particulate flow is allowed to proceed unchecked the producing wellbore soon becomes full of sand, thereby clogging oil production. Furthermore, particulate arriving at the surface of the well wears out the production hardware.
If has therefore been the subject of extensive research by the petroleum industry to develop techniques to minimize or obviate displacement of sand particles into producing well areas. One such general approach suggested in the art is to consolidate the porous particulate structures. Sand consolidation techniques are aimed at cementing loose sand structure adjacent a wellbore. Such consolidation is necessary to prevent breakdown of sand formations and subsequent clogging of producing wells.
The major feature of sand consolidation is to make a sieve next to the producing wellbore such that hydrocarbons can reach the wellbore while sand flow is retarded. The sieve is composed of formation particulate already present surrounding the wellbore area which is cemented together by consolidating material added to the formation. The consolidation need only be thick enough to prevent particulate breakdown adjacent to the wellbore. Ordinarily consolidation is effected for only a few inches around the periphery of the wellbore.
Accordingly, criteria for good consolidations are considered to be as follows. First, the consolidation structure should hold back formation particles while preserving high permeability. As consolidating material is added to the formation, this material will necessarily occupy part of the pore space causing permeability reduction. Therefore, an object of practical formation consolidation is to minimize occlusion of pore spaces so that hydrocarbons can flow to the producing wellbore.
Second, durability is a desired feature of a consolidation. The thin film of consolidating material holding the particulate should be physically durable in resisting deterioration by oil, water and other fluids in the formation.
Third, the consolidation action should not set up in the wellbore prematurely thereby occluding the wellbore path for hydrocarbon production.
Further, the consolidation operation should be simple, efficient and inexpensive. The economic significance of such an operation is great and the problems described above have been well recognized by the petroleum industry for many years. Many efforts have been made to satisfy these problems in whole or in part.
One particular approach to formation consolidation has been to inject into a well a polymerizable resin which polymerizes within the well formation. The polymer material forms a viscous mass which readily adheres to the porous particulate structures. As the particulate surfaces become coated, they no longer are subject to displacement when exposed to fluid flow. Unfortunately, the polymerization reaction is difficult to control so as to only consolidate the particulate without plugging the pore spaces and ultimately blocking permeability through the porous strata.
One of the better consolidating agents for high temperature wells is a polymerized furfuryl alcohol resin. The material resists heat as well as oil and water. The problem in using this material is in catalyzing the polymerization. If a delayed action catalyst is carried in a mixture containing the furfuryl alcohol oligomer, polymerization may occur too early causing wellbore blockage or too extensively so that permeability is lost; or alternatively, polymerization may not occur at all or be inadequate to effect consolidation.
Various processes for formation consolidation are disclosed in U.S. Pat. Nos. 3,536,137; 3,759,327; 4,042,032; 4,427,069 and 4,669,543, the entire disclosures of which are incorporated herein by reference.
The technique described by the present invention represents an improvement over the methods used previously in that polymerization and consequently the subsequent consolidation of the particulate in the formation is positively controlled in a manner whereby permeability of the formation is preserved.